1. Field of the Invention
The present invention relates to a developing device, a process cartridge in which a developing device and a photoconductor unit are integrated, and an image forming apparatus, and more particularly relates to an improved mechanism to prevent toner from leaking out of the developing device.
2. Discussion of the Background
There is known a developing device for developing an electrostatic latent image formed on a photoconductor in which a developing roller to supply toner to the photoconductor and a blade contacting a surface of the developing roller are mounted to a developing case containing toner therein. In such a developing device, the blade restricts the thickness of toner adhering to the developing roller. When single-component toner is used, the blade is pressed to contact the developing roller such that toner passing between the blade and the developing roller is charged by friction. When the blade is made of an elastically deformable metal plate the blade is fixed to the developing case and is pressed to the developing roller while being bent. In this case, because the rigidity of the blade is low, the blade is sandwiched between a blade holder with high rigidity and a supporting member so as to be laminated with each other, and the laminated blade, blade holder and supporting member are attached to the developing case.
If the developing device as described above is dropped during transportation, the developing roller and the blade vibrate and thereby toner intrudes into a gap between the backside of the blade and a blade attaching surface of the developing case and leaks out of the developing case. To prevent such leakage of toner, an opening of the developing case is sealed by a tape, which is peeled off when the developing device is used. This method of sealing an opening of a developing case with a tape requires an operation of taking off the seal when attaching the developing case to an image forming apparatus, which is troublesome.
In order to attach a blade made of a metal plate to a developing case, while laminating the blade with a long blade holder having high rigidity, a blade attaching surface corresponding to the long blade holder must be formed in the developing case. It is hard to form a blade attaching surface having a length corresponding to the long blade holder in a precise manner in the developing case. Generally, the blade attaching surface is formed partly uneven in the longitudinal direction and thereby the blade holder bends in the longitudinal direction together with the blade. Because of this bending of the blade holder and the blade, a contact line between the blade and the developing roller deviates from a line parallel to an axial line of the developing roller and thereby the contact pressure of the blade against the developing roller becomes uneven, causing an undesirable effect on the quality of a resulting image.
It may be conceivable to form protruding blade attaching surfaces in the vicinity of both ends of the developing case so as to support both ends of the blade holder, together with the blade, with the protruding blade attaching surfaces. However, the airtightness between the blade holder and the developing case is lost at the center part of the developing case, i.e., at a part between the blade attaching surfaces at both side ends of the developing case, and thereby toner tends to leak therefrom.
When a developing device is configured such that the amount of toner adhering to a developing roller is restricted by a blade, a roller part of the developing roller is disposed at a toner exit formed in a developing case and axial parts of the developing roller protruding from both ends of the roller part respectively are rotatably supported by supporting walls formed at both sides of the developing case. A lower edge of the blade contacts the roller part of the developing roller such that the blade seals a gap between an upper edge of the toner exit and an upper outer circumferential surface of the developing roller. Further, in order to prevent leakage of toner through a gap between an outer circumferential surface of the developing roller and the toner exit, side seals are provided at both longitudinal ends of the toner exit so as to contact outer circumferential surfaces of both ends of the roller part of the developing roller and an exit seal is provided at a flat surface of the developing case, which is formed in the developing case extending from a lower edge of the toner exit toward a photoconductor, so as to elastically contact the roller part of the developing roller.
In order to decrease the load to the developing roller when the developing roller is driven, the exit seal is generally formed with a thin plastic sheet having low compressibility and is configured such that a part of the exit seal is supported by the flat surface of the developing case and a free end part of the exit seal extending toward the toner exit from the flat surface is pressed against the outer circumferential surface of the developing roller by its own elasticity. The exit seal is generally stuck to the flat surface of the developing case by double-sided adhesive tape.
As described above, because the exit seal contacts the developing roller by its own elasticity and the part of the exit seal stuck to the flat surface of the developing case does not contact the developing roller, both ends of the exit seal tend to be peeled off. If both ends of the exit seal peel off, toner intruded under the exit seal intrudes toward both ends of the exit seal and may leak through a gap between the inner surfaces of the supporting walls formed at both sides of the developing case and the ends of the exit seal.
Further, in order to prevent leakage of toner through a gap between the outer circumferential surface of the developing roller and the toner exit, it is practiced that a free end side of an exit seal attached to a lower part of a developing case elastically contacts a lower outer circumferential surface of the developing roller and outer circumferential surfaces of both ends of a roller part of the developing roller are supported by side seals disposed at both longitudinal ends of the toner exit of the developing case.
When a blade is formed with a thin metal plate having elasticity and is configured such that the blade is bent by a developing roller so as to contact the developing roller by its reacting force when the blade is assembled in the developing device, as described above, the axial center of the developing roller is determined by a bearing of a developing case. In the above configuration, in order to bend the metal blade by pressure of the developing roller, the blade must be shorter than the interval between inner surfaces of side seals arranged at both sides of the developing roller. If the blade is made shorter than the interval between the inner surfaces of the side seals, a gap is generated between both ends of the blade and both inner surfaces of a toner exit, causing leakage of toner through the gap. If the blade is made longer than the interval between the inner surfaces of the side seals, the blade contacts the side seals due to pressure of the developing roller and thereby the blade cannot be bent any further. Such loss in the freedom of bending in the blade causes deformation of the blade and inferior sealing of a gap between the roller part of the developing roller and the side seals.
A known developing device includes a stirring device to stir toner in a developing case, a developing roller and a toner supplying roller to supply toner to the developing roller. In such a developing device, in order to transmit power to the toner stirring device and the toner supplying roller from the outside, rotation axes of these rotating devices protrude from a side wall of the developing case and gears are provided to ends of the protruded axes respectively to transmit rotation power to the axes.
In such a developing device, if sealing around the rotation axes of the stirring device and the toner supplying roller is insufficient, toner tends to leak out of the developing case around the rotation axes when the developing device falls and is shocked. The sealing effect around the rotation axes may be sufficiently increased by arranging a seal member having a rubber lip at respective inner circumferential parts of ring-shaped metal bearings supporting the rotation axes. However, the seal member having such a configuration is expensive and therefore increases the cost of a developing device using the sealing member.
In an image forming apparatus such as a copying machine or printer, it is widely practiced that a photoconductor unit, in which a photoconductor and a used toner collecting device to collect residual toner on an outer circumferential surface of the photoconductor are assembled in a body, and a developing device, in which a developing roller is provided to a developing case, are assembled to a unit known as a process cartridge.
FIGS. 19 and 20 illustrate an example of such a photoconductor unit. FIG. 19 is a side vertical cross section of a photoconductor unit 200. A photoconductor 9 is rotatably supported by the photoconductor unit 200 and a used toner collecting part 101 to collect used toner remaining on an outer circumferential surface of the photoconductor 9 is formed in the photoconductor unit 200.
FIG. 20 is a front view of the photoconductor unit 200 when the photoconductor 9 is removed. A collecting inlet 102 is formed in the used toner collecting part 101 at a position near an outer circumferential surface of the photoconductor 9. The collecting inlet 102 is formed in a long and narrow rectangular shape extending substantially over the entire length of the photoconductor 9. Side seals 103 formed with a teflon felt or the like are stuck at edges of both longitudinal sides of the collecting inlet 102. The side seals 103 slidably contact outer circumferential surfaces of both ends of the photoconductor 9.
A long blade 104 that scrapes off residual used toner on an outer circumferential surface of the photoconductor 9 is fixed to one longitudinal edge of the collecting inlet 102 and a long inlet seal 105 is stuck to the other longitudinal edge of the collecting inlet 102. The inlet seal 105 slidably contacts an outer circumferential surface of the photoconductor 9 so as to prevent used toner scraped off by the blade 104 from leaking through the collecting inlet 102. Both longitudinal ends of the inlet seal 105 contact the side seals 103 by pressure respectively.
The photoconductor 9 rotates in a direction indicated by an arrow in FIG. 19 and an electrostatic latent image is formed on an outer circumferential surface of the photoconductor 9 by exposure with a latent image forming part (not shown). The latent image is developed to a visible toner image with toner supplied by a developing roller (not shown), and the toner image is then transferred to a transfer sheet (not shown) at a transfer position. When the toner image is transferred to the transfer sheet, a part of the toner of the toner image is not transferred to the transfer sheet and remains on the outer circumferential surface of the photoconductor 9 as residual used toner. The residual toner is scraped off the outer circumferential surface of the photoconductor 9 with the blade 104 and is collected to the used toner collecting part 101. When collecting used toner, the inlet seal 105 slidably contacts the outer circumferential surface of the photoconductor 9 and thereby leakage of the collected used toner from the collecting inlet 102 is prevented. Also, leakage of toner from both sides of the inlet seal 105 is prevented by bringing both longitudinal ends of the inlet seal 105 into contact with the side seals 103 by pressure.
However, when the photoconductor 9 is rotated in the direction of the arrow in FIG. 19, a pulling force is applied to the inlet seal 105, which is slidably contacting the outer circumferential surface of the photoconductor 9, in the rotation direction of the photoconductor 9. The pulling force acts on both longitudinal ends of the inlet seal 105 in a direction to peel off the inlet seal 105 and thereby both ends of the inlet seal 105 are moved toward the center of the inlet seal 105 and thereby a part of the inlet seal 105 slidably contacting the outer circumferential surface of the photoconductor 9 waves. Because of this waving, a gap is created between the inlet seal 105 and the outer circumferential surface of the photoconductor 9 and collected used toner leaks through the gap.
Further, if a gap is created between the inlet seal 105 and the side seals 103, which are overlaid with each other, as a result of the both end parts of the inlet seal 105 being pulled toward the center of the inlet seal 105 as described above, collected used toner intrudes into the gap and the intruded toner leaks from the sides of the inlet seals 105.